Radiation source

ABSTRACT

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, or similar thermonuclear gas at a density of 10 17  to 10 20  electrons per cubic centimeter. The target gas is ionized prior to application of the relativistic electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy into a small localized region of the high-density plasma target.

BACKGROUND OF THE INVENTION

Fast liners disposed in the high-density target plasma are explosivelyor ablatively driven to implosion by a heated annular plasma surroundingthe fast liner generated by an annular relativistic electron beam. Anazimuthal magnetic field produced by axial current flow in the annularplasma, causes the energy in the heated annular plasma to converge onthe fast liner to implode the fast liner which can also be used toimplode a microsphere.

Additionally, the high-temperature plasma can be used to heat a high Zmaterial to generate radiation. Alternatively, a tunable radiationsource is produced by using a moderate Z gas or a mixture of high Z andlow Z gas as the target plasma.

The present invention pertains generally to dense plasma heating andmore particularly to plasma heating by way of a relativistic electronbeam to heat high Z materials to generate radiation.

Plasma heating has, for some time, been of great interest to thescientific community, since heated plasmas can be utilized for a widevariety of functions. A typical use of hot plasmas is the generation ofenergy in the form of radiation, neutrons, and alpha particles. Such anenergy source can be useful in basic high-energy density plasma physicsresearch, with practical application in scientific areas such ascontrolled thermonuclear fusion, material studies, and radiography.

Numerous techniques have been proposed in the prior art to producedense, kilovolt plasmas. One of the more well-known techniques is thecompression and heating of the core of a structured pellet by a laser orlow-voltage electron beam. It has also been suggested that light- orheavy-ion beams could be utilized to obtain similar compression andheating. According to this technique, the structured pellet and itsdriving source are directly coupled through classical interactions byheating the outer layer of the structured pellet. Depending upon thecharacteristics of both the structured pellet and driving source, theouter layer explodes or ablates, leading to compression and heating ofthe core. Due to the direct coupling of all of these prior art drivingsources, preheat of the core has been found to reduce the effectivenessof the compression, thereby reducing both density and temperature of thepellet core.

The use of a laser as a driving source in the above describedconfinement system has the added inherent disadvantages of lowefficiency and associated high-development cost to produce lasers withthe required power output for a directly driven structured pellet. Also,diffraction limitations and window damage thresholds make it difficultto focus proposed large lasers to millimeter diameters.

Low-impedance electron and light-ion beams also face expensivetechnological advancement to enable these beams to be focused tomillimeter diameters, and to obtain power levels necessary to achievethe desired compression of the structured pellet. Low-impedance electronand light-ion sources are additionally limited in the manner ofpropagation of the beam to the pellet.

Heavy-ion sources also require significant technological advancement toproduce the desired compression of the structured pellet. In fact,development of heavy-ion sources using conventional accelerator conceptsappears to be considerably more expensive than the cost associated withthe development of lasers. Beam propagation is also a limitation whenemploying heavy-ion sources.

High-density, kilovolt plasmas can also be produced by fast liners. Suchdevices can be driven by either magnetic forces or high explosives, bothof which lead to compression and heating of a confined plasma. Althoughboth of these fast liner techniques have produced energy in the form ofradiation, neutrons, and alpha particles, each technique has its owninherent disadvantage. The primary disadvantage of the high explosivedriven liner is that the high explosives have a maximum power density ofapproximately 10¹⁰ watts/cm³ and a maximum detonation velocity of8.8×10⁵ cm/sec, which limits achievable liner implosion velocity.Although useful in obtaining scientific data, such a system would bedifficult to develop into a reuseable apparatus.

Magnetically driven liners are fabricated such that the liner forms partof the electrical discharge circuit in which current flowing through theliner creates a large magnetic field causing the liner to compress.Since the liner forms part of the electrical circuit, the externalcircuit resistance and finite liner resistivity lead to ohmic losseswhich lower the efficiency of converting electrical energy into linerkinetic energy. Also, since the liner must make electrical contact withthe circuit, damage to the electrode connection between the moving linerand the electrode limits operability.

For liners which essentially remain thin solid shells during theimplosion, ohmic heating and magnetic field diffusion limits implosionvelocities to approximately 1 cm/μsec. To obtain the desired radiation,neutron, and alpha particle output at such low implosion velocities, theplasma within the liner must be preionized and complex methods ofovercoming heat conduction losses must be incorporated into the system.

Although liner implosion velocities exceeding 1 cm/μsec can be achieved,ohmic heating and magnetic field diffusion converts solid liners intoplasmas during operation. As a result, the thickness of the liner isincreased, which lowers the potential for power multiplication. Evenwith very thin foils, implosion velocities are limited by the risetimeof the driving current and diffusion of the driving magnetic fieldthrough the plasma liner.

Lasers have also been used to directly heat a magnetically confinedplasma. According to this concept, a laser is used to heat a largevolume of plasma confined by an elaborate magnetic field system tothermonuclear temperatures. Although the laser provides uniformionization and rapid heating of a low-temperature plasma, thecharacteristic deposition length increases approximately as T^(3/2) forplasma electron temperatures T>10 eV. This characteristic of thedeposition of laser energy in the plasma, coupled with the large volumeof plasma to be heated, places a total energy requirement for the laserwhich substantially exceeds present technology. Even in such laserscould be developed, the inherent low efficiencies associated withgeneration of laser energy would result in a large-capital investmentfor such a system.

A similar system incorporates a light- or heavy-ion beam to deposit itsenergy in a magnetically confined plasma. Since such beams arenonrelativistic, they exhibit a very low coupling efficiency and lackversatility obtainable by the relativistic interaction.

The concept of using an intense relativistic electron beam to heat aconfined plasma has been investigated experimentally for a number ofyears. Prior art experiments have concentrated primarily on heating alarge volume of plasma to thermonuclear temperatures with an electronbeam, while maintaining the plasma with an external magnetic field. Atypical configuration of a prior art experimental apparatus is shown inFIG. 1. A cathode 10 is positioned within a vacuum chamber 12 which isseparated from the plasma chamber 14 by an anode foil 16. A series ofdielectric spacers 18 are separated by a series of metal plates 20,which function together to prevent breakdown between the cathode 10 andthe diode support structure 22. A solenoidal or mirror magnetic fieldconfiguration 24 is produced by an external source.

In operation, a relativistic electron beam 26 is formed by charging thecathode 10 with a fast risetime high-voltage pulse, causing electrons tobe field emitted from the cathode 10 penetrating the anode foil 16 so asto enter the plasma chamber 14 as a relativistic electron beam 26. Asthe relativistic beam propagates through the plasma along the externallyapplied axial magnetic field 24, the plasma is heated by the followingmethods:

(a) relaxation heating due to relativistic streaming instabilities(two-stream and upper-hybrid bunching instabilities); and,

(b) anomalous resistive heating due to the presence of a plasma returncurrent (ion-acoustic and ion-cyclotron instabilities).

Typically, devices such as klystrons, magnetrons, vacuum tubes, etc.,which are based upon electron bunching according to method (a) have beenconsidered very efficient devices with respect to energy utilization.Therefore, the process of heating a plasma by electron bunching, i.e.,by generating the two-stream and upper-hybrid instabilities according tomethod (a), was initially expected to be an efficient technique forproducing a thermonuclear plasma. Although all early experimentsobserved anomalous (nonclassical) coupling of the beam energy to theplasma resulting from the presence of the streaming instabilitiesaccording to the method (a), the coupling efficiency was only on theorder of 15% at plasma densities of approximately 10¹² electrons/cm³,and dropped rapidly to less than a few percent as the plasma densityapproached 10¹⁴ electrons/cm³. These results were obtained with anodefoils having thicknesses on the order of 25 μm to 50 μm and conventionalelectron beams available for experiments during this period whichtypically had relatively low voltages, i.e., 1 MeV or less. Thiscombination of relatively thick anode foils and low-voltage beamsresulted in classical anode foil scattering of the beam which preventedthe relativistic streaming instabilities from efficiently coupling thebeam energy to the plasma. In other words, although unknown to theexperimentalists and theoreticians during the period 1970-1975, the foilthickness and low voltage of the electron beams used in the experimentscaused the electron beam to scatter in a manner which preventedsubstantial electron bunching in the beam. This, in turn, produced theobserved rapidly decreasing energy absorption efficiencies as the plasmadensity approached 10¹⁴ electrons/cm³. As a result of these low observedefficiencies, scientific attention shifted toward investigation of theresistive heating mechanism according to method (b), which has known tohave several scientifically interesting properties.

One property of the resistive heating mechanism of method (b) is itsability to place a substantial fraction of the beam energy into plasmaions. This differs from the streaming instabilities which primarily heatthe plasma electrons. Since the ions must eventually be heated in amagnetically contained plasma, according to conventional magneticconfinement systems, direct heating of the ions eliminates an energyconversion step. Furthermore, when energy is initially deposited intoplasma electrons rather than the ions, heat conduction is enhanced dueto the initially elevated electron temperature, so that achievableplasma confinement time is shortened. Consequently, increased magneticfield strengths are required to produce comparable confinement.

Another property of the resistive heating mechanism is its ability toheat a large volume of plasma in a uniform manner, rather thandepositing energy in a small localized region, as is characteristic ofthe optimized streaming instability mechanism. The ability to directlyheat a large volume of plasma in a uniform manner by resistive heatingthus avoids problems of heat redistribution within the plasma. Moreover,the potential for developing a plasma heating system which could also beused in conjunction with devices requiring preheated plasmas, such astokamaks which have received substantial funding, renders the resistiveheating mechanism even more attractive. For these reasons, experimentalattention was directed from the onset of plasma heating experimentsusing relativistic electron beams towards producing resistive heating inplasmas according to method (b). Consequently, experimental apparatus tooptimize resistive heating effects, such as low-voltage electron beamswith high ν/γ outputs, were utilized in ongoing experiments ofrelativistic electron beam heated plasmas. Here, γ is the beamrelativistic factor which is nearly proportional to the beam particlevoltage. The ratio ν/γ is basically a measure of the beam self-magneticfield energy to beam particle energy. The increased use of high ν/γbeams is more graphically shown in FIGS. 2 and 3 which illustrate thedecrease in maximum beam voltage and increase in maximum ν/γ forrelativistic electron beam experiments between 1970 and 1975. Thus theprior art experiments have, from the beginning, concentrated on highν/γ, low-voltage beams for optimizing the resistive heating mechanismaccording to method (b), virtually ignoring the effect of streaminginstabilities produced according to method (a).

In so doing, prior art experiments, have clearly pointed out thelimitations of resistive heating according to method (b), i.e., thatresistive heating does not scale to higher density plasmas, but, to thecontrary, is absolutely limited by selfstabilization within the plasma.More particularly, the experiments have shown that above a certainelectron temperature, depending on the density of the plasma,low-frequency instabilities which are responsible for resistive heating,are stabilized. Consequently, only classical resistivity, which isinadequate to couple significant energy to the plasma from therelativistic electron beam, has any effect in resistively heating theplasma.

In addition to this inherent stabilization limitation, the technique ofresistive heating has several other disadvantages. First, even ifexperiments had shown that resistive heating according to method (b) waseffective at high plasma density, the required ν/γ for efficientcoupling would be at least an order-of-magnitude higher than thatachievable by present day technology. Second, since resistive heating isonly suitable for low plasma densities which are very large in volume,the total energy required to heat such a plasma would again, be at leastan order-of-magnitude beyond the total beam energy achievable by presenttechnology standards.

As a result of these limitations, and the belief by prior arttheoreticians and experimentalists that resistive heating dominatedanomalous energy deposition in plasmas, the relativistic electron beamplasma heating program in the United States was virtually abolished in1975 without any further investigation into the streaming instabilityheating mechanism.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages and limitations of theprior art by providing a device and method for electron beam heating ofa high-density plasma to heat a high Z material to generate radiation orheating a moderate Z gas or high Z has mixed with a low Z gas to produceradiation. The present invention utilizes either an annular or solidrelativistic electron beam to heat a plasma to kilovolt temperaturesthrough streaming instabilities in the plasma. Energy deposited in theplasma then heats a high Z material, such as a wire array, to generateradiation. Heating of a moderate Z gas or mixture of a high Z gas with alow Z gas can be performed with either a solid or annular relativisticelectron beam.

It is therefore an object of the present invention to provide a deviceand method for generating a hot plasma to generate radiation directly orheat a high Z material to generate radiation.

It is also an object of the present invention to provide a device andmethod for generating intense radiation which is efficient in operation.

Another object of the present invention is to provide a device andmethod for generating radiation.

Another object of the present invention is to provide a device andmethod for generating radiation which requires relatively low-capitalinvestment.

Another object of the present invention is to provide a device andmethod for generating high-intensity radiation utilizing currentlyavailable technology.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter. The detailed description, indicating the preferredembodiment of the invention is given only by way of illustration sincevarious changes and modifications within the spirit and scope of theinvention will become apparent to those skilled in the art from thedetailed description. The foregoing abstract of the disclosure is forthe purpose of providing a nonlegal brief statement to serve as asearching and scanning tool for scientists, engineers, and researchersand is not intended to limit the scope of the invention as disclosedherein, nor is it intended to be used in interpreting or in any waylimiting the scope or fair meaning of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a typical prior art relativsticelectron beam plasma heating device.

FIG. 2 is a graph of maximum experimental relativistic electron beamvoltages utilized from 1970 to 1975.

FIG. 3 is a graph of maximum experimental ν/γ of relativistic electronbeams utilized from 1970 to 1975.

FIG. 4 is a graph illustrating the characteristic relationship betweenthe relativistic electron beam and plasma ions and electrons forresistive heating according to method (b). The graph illustrates thecomponent of velocity along the direction of beam propagation V.sub.∥(axis) versus the distribution function f_(a) (V.sub.∥) (ordinate).

FIG. 5 is a graph illustrating the characteristic relationship betweenthe relativistic electron beam and plasma ions and electrons forrelaxation heating according to method (a) of the present invention. Thegraph illustrates the component velocity along the direction of beampropagation V.sub.∥ (axis) versus the distribution function f_(a)(V.sub.∥) (ordinate).

FIG. 6 is a graph illustrating the characteristic nonuniform energydeposition (ordinate) along the direction of beam propagation (axis)associated with the streaming instabilities of method (a). Aone-dimensional interaction is represented by the solid line while thedashed line represents a two-dimensional interaction.

FIG. 7 is a graph of the experimental scaling of plasma heating injoules (ordinate) versus the plasma particle density n_(p) inelectrons/cm³ for three different anode foil thicknesses. Theoreticalpredictions are indicated by solid curves.

FIG. 8 is a graph illustrating experimental results of beam energytransmitted to a calorimeter (ordinate) versus anode foil thickness forthree different anode-cathode gap spacings.

FIG. 9 is a table of the foil scattering function F for seven differentmaterials having various thicknesses measured in microns.

FIG. 10 is a graph of the dimensionless parameter Γ (ordinate) versusthe relativistic factor γ (axis) for given values of plasma density inelectrons/cm³.

FIG. 11 is a schematic diagram illustrating the primary components of asystem utilizing high-energy density plasma as a direct source ofradiation.

FIG. 12 is a schematic diagram illustrating the primary components of asystem which utilizes a high-energy density plasma to produce radiationaccording to the peferred embodiment of the invention.

FIG. 13 is a schematic illustration of a two annular beam systemproviding cylindrical symmetry.

FIG. 14 is a schematic illustration of a two annular beam systemproviding spherical symmetry.

FIG. 15 is a schematic illustration of a four annular beam system whichalso provides spherical symmetry in a multimegajoule system.

FIG. 16 is a schematic diagram illustrating the relative sizes ofvarious relativistic electron beam generators relative to a 1.83 meterindividual.

FIG. 17 is a graph illustrating the approximate cost per joule delivered(ordinate) as a function of total generator cost in thousands of dollars(axis).

FIG. 18 is a schematic illustration of the basic components of ahigh-impedence relativistic electron beam generator.

FIG. 19 is a schematic illustration of the electrical equivalent of aMarx stage.

FIG. 20 is a schematic illustration of the electrical equivalent of aBlumlein and diode.

FIG. 21 is a schematic illustration of a multigap accelerator.

FIG. 22 is a graph of the characteristic growth rate and velocity change(ordinate) as a function of wave number for the streaming instabilities(axis).

FIG. 23 is a schematic illustration of an anomalous pinch.

FIG. 24 is a schematic illustration of a device for producing ananomalous pinch utilizing a single laser preionizer.

FIG. 25 is a schematic illustration of a device for producing ananomalous pinch utilizing two laser preionizers.

FIG. 26 is a schematic illustration of the end view of a device forproducing an anomalous pinch utilizing three laser preionizers.

FIG. 27 is a schematic illustration of the basic geometry of a devicefor driving a fast sperical liner with an annular relativistic beam.

FIG. 28 is a schematic illustration of the basic geometry for driving afast cylindrical liner with an annular relativistic electron beam.

FIG. 29 is a schematic cross-sectional view of a spherical linerconfiguration with dual ionization beams.

FIG. 30 is a schematic illustration of a cross-sectional view of acylindrical liner configuration with dual ionization beams.

FIG. 31 is a schematic illustration of a cross-sectional view of a fastspherical liner.

FIG. 32 is a schematic illustration of a cross-sectional view of a fastcylindrical liner.

FIG. 33 is a schematic illustration of a cross-sectional view of analternative fast liner device.

FIG. 34 is a schematic illustration of the target geometry utilizing twoannular relativistic electron beams to drive a spherical liner, in themanner in FIG. 14.

FIG. 35 is a schematic illustration of the basic geometry for fastspherical liner implosion of a structured microsphere.

FIG. 36 is a schematic illustration of the basic geometry for fastcylindrical liner implosion of a structured microsphere.

FIG. 37 is a schematic illustration of a cross-sectional view of a fastspherical liner and a structured microsphere.

FIG. 38 is a schematic illustration of a cross-sectional view of a fastcylindrical liner and a structured microsphere.

FIG. 39 is a schematic cross-sectional view of a wire array device forradiation generation.

FIG. 40 is a schematic end view of a wire array device for radiationgeneration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Central to the concept of the preferred embodiment of the invention isthe rapid heating of a 10¹⁷ -10²⁰ electron/cm³, 3 cm³ to 50 cm³ ofplasma by an intense, high-voltage relativistic electron beam. Efficientcoupling is achieved through optimization and control of a very powerfulcollective wave interaction, which occurs naturally when a directedstream of electrons passes through a plasma.

The anomalous transfer of relativistic electron beam energy and momentuminto thermal and directed plasma energy, respectively, is nonclassicaland, therefore, the strength of the nonlinear state of themicroinstabilities depends upon a large number of factors. Thecharacteristic nonuniform energy deposition of the collectiveinteraction is utilized to concentrate the energy in the plasma. Infact, the optimized relativistic electron beamplasma interaction is apower density multiplication process. Since energy is being transferredfrom relativistic beam electrons to nonrelativistic electrons in theplasma, conservation of energy and momentum require that the interactionboth heat and drive a localized axial current in the plasma. The drivenaxial current, in turn, generates an azimuthal magnetic field.

If the relativistic beam is solid, the physical configuration is similarto a nonuniform dense Z pinch in which the azimuthal magnetic fieldprovides confinement. However, in contrast to a classical Z pinch, theheating and confinement are anomalous in character. For an annularrelativistic electron beam, the azimuthal magnetic field leads to adirected heat flow towards the axis of the device. In thisconfiguration, the kilovolt plasma is used to heat a high Z materialsuch as a wire array to generate radiation according to the presentinvention.

Early theory by R. V. Lovelace and R. N. Sudan, Phys. Rev. Letter 27,1256 (1971), indicated that resistive heating according to method (b)was a very efficient process for beams with ν/γ>>1. As pointed outabove, ν/γ is a measure of the beam self-magnetic field energy to thebeam particle energy. Defining N as the line density of beam electronsand r_(e) as the classical electron radius, ν.tbd.Nr_(e) for a solid,constant density beam. The relativistic factor γ=(1-β²)^(-1/2) and β=v/care, in this manner, related to the beam velocity v and speed of lightc. The basic idea behind anomalous resistive heating is that a ν/γ>>1beam cannot propagate since its self-magnetic field energy exceeds itsparticle energy. But, when such a beam is injected into a plasma, itneutralizes this characteristically large self-magnetic field energy byinducing a plasma return current. The relationship between the plasmaand beam species in velocity space for a magnetically neutralized beamis shown in FIG. 4. Due to the relative drift between the plasmaelectron and ion species, ion-acoustic and/or ion-cyclotron waves aregenerated, as illustrated in FIG. 4 by the dashed lines. Suchmicroturbulence is known to manifest itself as anomalous resistance.Thus, the plasma is heated at a rate

    dW.sub.p /dt=η*J.sub.p.sup.2,                          (1)

where W_(p) is the plasma energy density, η* is the anomalousresistivity, and J_(p) is the plasma return current density. At the sametime, the macroscopic electric field which maintains the return current,in order for the beam to propagate, removes energy from the beam. Inthis fashion, energy is transferred from the beam and deposited intoplasma electrons and ions.

In contrast to resistive heating described above, relaxation heatingaccording to method (a) results from the relative drift between therelativistic beam electrons and plasma electrons. Optimally, theseinstabilities take the form of electron bunching at a wavelength of

    λ≅(1-4)[10.sup.20 /n.sub.e (cm.sup.-3)].sup.1/2 μm (2)

and a frequency of

    f≅[n.sub.e (cm.sup.-3)/10.sup.16 ]THz,           (3)

where n_(e) is the plasma electron density. The characteristicrelationship between the plasma and beam species for optimizedrelaxation heating is illustrated in FIG. 5. Locally, the net currentI_(net) within the beam channel can exceed the beam current I_(b), incontrast to the magnetically neutralized beam where I_(net) ≅0 withinthe beam channel. As stated, this current multiplication is aconsequence of momentum conservation, and is a very localizedphenomenon. The location of the unstable spectrum for theseinstabilities is indicated by dashed lines in FIG. 5.

The present invention, in contrast to prior art plasma heatingtechniques takes advantage of the natural characteristics of twoextremely powerful microinstabilities, i.e., the two-stream andupper-hybrid instabilities illustrated in FIG. 5, to locally heat amoderate Z or mixture of low Z and high Z plasma to generate radiationdirectly. Alternatively, the relativistic electron beam is used to heata high-density plasma to kilovolt temperatures to heat a high Z materialsuch as a wire array to generate radiation. In both embodiments, theradiation can take the form of x-rays. Essentially, the instabilitiesare created by the relative drift between the relativistic beamelectrons and target plasma electrons. Although a large number ofparameters influence this collective interaction, the dominant factorsin determining the strength of the instabilities are (1) beamtemperature along a streamline, and (2) the wavelength of theinstabilities relative to the radial dimension of the target plasma.

In prior art experimentation, beam temperature along a streamline occursprimarily from the passage of the relativistic electrons of the beamthrough the foil dividing the low-density plasma and diode vacuum. Theeffect of the foil can be made negligible by (1) increasing the electronenergy, (2) reducing the thickness of foil, or (3) reducing theeffective Z of the foil material. As a result, a high-voltage, i.e.,exceeding 3 MeV, electron beam can, in fact, penetrate a number of foilsand still deposit its energy efficiently in the high-density plasma.

By utilizing plasmas of high-density, the wavelength of theinstabilities are small compared to the radial dimensions of the plasma.Thus, although the instantaneous deposition rate can vary, the nonlinearevolution of the instability functions to relax the beam distribution inboth angle and energy, resulting in an efficient coupling of beam energyto the plasma.

The characteristic nonuniform energy deposition of the collectiveinteraction, i.e., two-stream and upper-hybrid instabilities along thedirection of beam propagation, is illustrated in FIG. 6. Aone-dimensional interaction is represented by the solid line while thedashed line represents a two-dimensional interaction. This nonuniformdeposition property is utilized to concentrate energy deposited into theplasma from the relativistic electron beam, rather than allowing theenergy to dissipate its explosive character by expansion into a largevolume of plasma. The initial deposition of beam energy is into plasmaelectrons which, depending upon the parameters of the device, results,in (1) heat conduction which is used propitiously to obtain powermultiplication, or in (2) current multiplication and confinement of theplasma. In this manner, the disadvantages of preferential heating ofplasma electrons associated with magnetically confined plasmas isadvantageously employed in the present invention.

The potential efficiency of relativistic beam energy deposition into adense plasma via the streaming instability mechanism has hertofore beenunknown in the prior art. FIG. 7 illustrates results of recentexperiments performed according to the present invention in which energydeposition is plotted against plasma density for the application of arelativistic beam through anode foils having various thicknesses. As isapparent from the data of FIG. 7, a reduction in the anode foilthickness causes a great increase in deposition energy into the plasma.These results show that the basic coefficient of coupling α of thestreaming instability deposition varies in the following manner:

    α=χS[1-exp(-χS/F)]/(1+χS)                (4)

where S.tbd.β² γ(n_(b) /2n_(e))^(1/3) is the strength parameter, F is afunction depending upon the foil thickness and material, n_(b) is thebeam density, n_(e) is the plasma electron density, and χ=1.0-1.3 is aparameter associated with beam premodulation.

It is therefore apparent from efficiency equation (4) that if either thebeam voltage (γ) is increased, or the foil function (F) reduced bydecreasing the foil's effective Z or thickness, the factor exp(-χS/F)approaches zero, such that the efficiency increases in direct proportionto χS/(1+χS). Thus, the coupling efficiency is large for high-densityplasma targets when high-voltage beams are utilized. Moreover, thesecoupling efficiencies can be obtained with little or no advancement inpresent relativistic electron beam technology since beams with voltageparameters sufficiently high to practice the present invention presentlyexist. As a result, currently available high-voltage relativisticelectron beams are capable of achieving high energy deposition due tothe ability of the high-voltage beams to penetrate the anode foil withreduced electron beam scattering. Thus, beams with ν/γ≲1 achieve muchhigher coupling efficiencies via the streaming instabilities than beamswith ν/γ>>1 which are designed to optimize the resistive heatingmechanism when using high-density plasma targets.

FIG. 8 illustrates results of an additional experiment showingpropagation distance in a high-density plasma with various foilthicknesses and anode-cathode gap spacing. In this experiment a 7 MeVbeam was injected into a 43 cm long, 0.4 torr H₂ gas target. No externalmagnetic field was present. The beam energy transmitted to a calorimeterlocated 43 cm from the anode foil was measured as a function of theanode-cathode gap spacing and anode foil thickness. Anode foils of 25.4μm kapton and 25.4 μm, 76.2 μm, 127.0 μm, and 304.8 μm titanium wereused. FIG. 8 shows a strong experimental dependence of the transmittedbeam energy on the anode thickness and anode-cathode gap spacing. Tencentimeter long witness plates starting at the anode foil on the bottomof the gas container showed significant damage when the kapton foil wasused, but showed little or no damage when the thicker titanium foilswere used. The distortion of the anode foil was also found to dependdramatically upon foil thickness. Independent of foil thickness, thecenter region through which the beam passed was completely gone.However, the observed debris protruded in the direction of beampropagation for the thicker titanium foils, while the kapton foil showeddebris protruding in the opposite direction. These results indicateformation of hot plasma in the vicinity of the thin foils and severedisruption of beam propagation as foil scattering is reduced due to amechanism which depends upon microscopic properties of the beamdistribution function. Furthermore, the distance over which such adisruption occurs is approximately 5 to 10 cm with the kapton foil,while the classical range for a 7 MeV electron in 0.4 torr H₂ gas isapproximately 10⁴ meter. These observations, as well as the scaling withthe anode-cathode gap, illustrate the effect of the streaminginstability.

The basic dependence among the beam relativistic factor γ=(1-β²)^(-1/2),beam particle density n_(b), and plasma electron particle density n_(e),is given by the strength parameter S=β² γ (n_(b) /2n_(e))^(1/3). Thepotentially large coupling efficiency associated with the relativisticstreaming instabilities is a consequence of the relativistic dynamics,the strength of which depends upon S. Specifically, if an electronundergoes a change in velocity δβ=δv/c, its change in energy is δγ=γ³βδβ/(1+γ² βδβ). For the streaming instabilities, the characteristicchange in velocity incurred during bunching is δβ≅γ⁻¹ (n_(b)/2n_(e))^(1/3) β. It follows that

    δγ/γ≅S/(1+S),                  (5)

which can be of order unity.

A more detailed one-dimensional analysis indicates that not all the beamelectrons act coherently during the bunching process, since theirindividual responses vary with energy. Basically, this is due to phasemixing. Denoting α as the coupling coefficient, the one-dimensionalanalysis yields

    α=1.5 S/(1+1.5 S).sup.5/2,                           (6)

which maximizes at S≅0.45 with α≅0.19. This rather high optimumefficiency for a one-dimensional analysis is still believed to be themaximum efficiency obtainable by the great majority of the plasmaphysics community.

In reality, the assumption that the nonlinear state is one-dimensionalas shown by the solid line in FIG. 6, is physically incorrect for anoptimized interaction and more clearly resembles the dashed line of FIG.6, which is the result of a two-dimensional analysis. Since therelativistic electron beam will relax strongly in both energy and angle,it is necessary to carry out a self-consistent, two-dimensional, fullyrelativistic nonlinear calculation to determine the couplingcoefficient. Such calculations can only be carried out using advancedparticle code techniques. Because such codes are expensive to run andcannot be employed for all physical parameter regimes of interest, ananalytical procedure or model has been developed which determines themagnitude of various parameters for optimal interactions which isdisclosed in Los Alamos Scientific Report LA-7215-MS (April 1978) byLester E. Thode entitled "Preliminary Investigation of AnomalousRelativistic Electron Beam into a 10¹⁷ to 10²⁰ cm⁻³ Density Plasma"available at the Library of Congress. From this model and extensivenumerical particle simulations, the phase mixing present in theone-dimensional analysis can be overcome by the angular relaxation ofthe beam, and an optimal coupling efficiency of

    α.sub.optimal ≅S/(1+S)                     (7)

appears achievable.

The factors which influence the coupling coefficient include thefollowing:

(1) beam relativistic factor,

(2) beam particle density,

(3) plasma particle density,

(4) beam temperature along a streamline,

(5) Larmor radius effects resulting from radially dependent orderedtransverse motion,

(6) wavelength of instability relative to radial size of the beam andplasma,

(7) radial plasma gradients,

(8) externally applied magnetic field strength,

(9) plasma temperature,

(10) electron-ion and electron-neutral collision rate,

(11) ionization state of plasma and ionization gradients,

(12) plasma hydrodynamic gradients,

(13) beam pinching resulting from current multiplication,

(14) premodulation, and

(15) time dependence of the electron beam power.

It has been found that the electron random motion or temperature along astreamline and the wavelength of the instabilities relative to theradial size of the plasma primarily determines the ability of theinteraction to sustain a high coupling efficiency over the entire beampulse, as pointed out above.

Beam temperature along a streamline can result from the random motionassociated with the temperature of the cathode surface. However,transverse temperatures of 300-1000 eV at the emission surface arerequired before this source of random motion begins to degrade theinteraction. Due to the high-voltage applied to the cathode, electronsare field emitted with typical transverse energies of 1 to 20 eV. Thus,this source of random motion is negligible in the invention.

A possibly more serious source of random motion is electron emissionfrom the cathode shank and lack of beam equilibrium at the emissionsurface. However, by shaping the cathode and anode surfaces properly,and by simultaneously applying an external magnetic field to the dioderegion, this source of random motion can also be reduced to a negligiblelevel.

In fact, beam temperature along a streamline seems to result primarilyfrom the passage of realtivistic electrons through thin foils. Extensiveanalysis has shown that the effect of such a foil on the interaction canbe made negligible. The effect of a foil is to reduce the fraction ofbeam electrons Δn/n_(b) which can act coherently during the developmentof the instability. This fraction is determined as follows:

    Δn/n.sub.b =1-exp(-χS/F).                        (8)

Typical values for the foil scattering function (F) are given in thetable of FIG. 9. It follows that increasing γ and decreasing the foil'seffective thickness results in the factor exp(-χS/F) approaching zero.Thus, the beam can penetrate a closed container and retain a highcoupling efficiency to the enclosed target plasma.

It has generally been argued that the transverse motion associated withthe beam self-fields comprises an effective temperature. If no externalmagnetic field is present and the beam is injected into a plasma inorder to obtain equilibrium, such ordered motion can evolve into randommotion. However, for the optimized interaction, the coherence length ofthe beam is long relative to the deposition length. Thus, high-voltage,low ν/γ beams in a focused flow configuration can interact strongly witha plasma, provided the plasma begins at the anode foil and Δn/n_(b) ≅1.

If the target plasma is also high-density, the wavelength associatedwith the streaming instabilities is very short compared to the radialdimensions of the beam and plasma, Eq. (2). Under these conditions, theoptimal nonlinear evolution of the instability is highlytwo-dimensional, and once initiated is extremely difficult to degrade.The formation of plasma hydrodynamic gradients and beam pinching due tocurrent multiplication results in the instantaneous deposition ratevarying in time. Such a time variation is not monotonic, however.

The distance over which the relativistic electron beam can depositupwards of S/(1+S) of its kinetic energy is

    L.sub.N ≅10γ(n.sub.e /n.sub.b).sup.1/3 c/ω.sub.p, (9)

where ω_(p) is the target plasma frequency and c is the speed of light.This is order's-of-magnitude shorter than the classical range ofmegavolt electrons in a 10¹⁷ -10²⁰ cm⁻³ density plasma. For example, ifn_(b) (γ) is determined from one-dimensional, relativistic foil dioderesult, such as disclosed by H. R. Jory and A. W. Trivelpiece, J. Appl.Phys. 40, 3924 (1969),

    L.sub.N ≅Γ(γ)(d.sup.2 /M).sup.1/3 cm. (10)

In Eq. (10) the diode gap spacing is d and the adiabatic compressionratio is M. The dimensionless parameter Γ(γ) is shown for given valuesof the plasma electron density n_(e) in FIG. 10. Because waves e-foldfrom noise, most of the beam energy is actually deposited over a lengthshorter than L_(N) by a factor of 2 to 3. The characteristic nonuniformenergy deposition of the collective mechanisms, two-stream andupper-hybrid instabilities, is shown in FIG. 6, for both the one- andtwo-dimensional interactions. According to the present invention, thisnonuniform deposition property is utilized to concentrate energydeposited into the plasma from the relativistic electron beam, asopposed to prior art experimentation wherein energy is allowed todissipate its explosive character by expansion into a much larger volumeof plasma.

Two basic approaches for utilizing a relativistic electron beam driven,high-energy density plasma to produce radiation, neutrons, and/or alphaparticles are possible.

The first approach is a direct use of the plasma as the source byconfining its energy for a sufficient length of time as disclosed incopending application Ser. No. 882,024 entitled "Device and Method forElectron Beam Heating of a High Density Plasma" filed Feb. 28, 1978 byLester E. Thode. According to this approach, a solid relativisticelectron beam penetrates a 3 cm³ to 50 cm³ gas filled container, andtransfers a fraction of its energy and momentum to the enclosed gas.Conservation of energy and momentum requires that the beam both heat theplasma and drive a large axial plasma current. The presence of the largeaxial current, in turn, initiates additional plasma ion heating andconfinement. This configuration is similar to a dense Z-pinch. At highplasma density the option for predominantly heating electrons or heatingboth electrons and ions exists. This is possible because the classicalequipartition time between the plasma species and the anomalous electronand ion heating rates can be varied significantly. FIG. 11 discloses aschematic diagram of the major components of a device which uses thehigh-energy density plasma as a source.

According to the second approach as disclosed in copending applicationSer. No. 9,703 entitled "Device and Method for Relativistic ElectronBeam Heating of a High-Density Plasma to Drive Fast Liners" filed Feb.5, 1979 by Lester E. Thode and copending application Ser. No. 9,702entitled "Device and Method for Imploding a Microsphere with a FastLiner" filed Feb. 5, 1979 by Lester E. Thode, an annular relativisticelectron beam is utilized to penetrate a 3 cm³ to 50 cm³ gas filledcontainer, and to transfer a fraction of its energy and momentum to theenclosed gas. Again, conservation of energy and momentum causes the beamto both heat the plasma and drive a large axial plasma current. Sincethe heated plasma is annular, the large axial current leads to directedheat flow towards the interior of the annular region, where a fast lineris disposed which is engulfed and driven inwardly by hot electrons toimplode on itself or to implode a structured microsphere. The fast linerfunctions as a power multiplier, which is cylindrical, spherical, orellipsoidal in shape. By adjusting the electron heating rate and plasmadensity, the device can be driven by either ablation or explodingpusher. Also, control of the driving electron temperature anddistribution is accomplished by varying the plasma density and magnitudeof the external magnetic field. A conceptual diagram of the majorcomponents of a system to utilize a high-energy density plasma to drivepower multiplication conversion devices is shown in FIG. 12.

According to the approach of the present invention, radiation isproduced in two ways. The first way involves heating either ahigh-density moderate Z plasma, or a high-density, high Z plasma mixedwith a low Z plasma, by either a solid or annular relativistic electronbeam. The second way comprises heating a high-density, low Z plasma asset forth above and using the heated plasma to heat a high Z materialsuch as a wire array as illustrated in FIGS. 39 and 40. Although anannular beam is shown in FIGS. 39 and 40, a solid beam can also be usedwith the inner wire array eliminated.

Many modifications and variations of the configurations shown in FIGS.11 and 12 are possible. For example, various applications of the conceptdo not require the use of a low-density gas chambers 52 and 94,modulators 38 and 80, drift tubes and adiabatic compressors 36 and 78,or multigap accelerators 32 and 74. With advances in relativisticelectron beam technology, external magnetic field sources 70 and 110,preionizers 62 and 64, 104 and 106, and windows 54 to 60, and 96 to 102can be eliminated. With annular beams, multiple beam systems arepossible, as depicted in FIGS. 13 through 15. For multiple beam systems,the energy deposition regions do not overlap, allowing such systems todrive larger power multiplication devices.

To practice the present invention, a high-voltage, high-current densityrelativistic electron beam is required for the reasons set forth above.Presently, a number of high-impedance generators are in use, such as thePI23-100, PI15-90, PI14-80, and PI9-50 which are schematicallyillustrated in FIG. 16. Here, PI refers to the Physics InternationalCompany, the first number is the diameter of the Blumlein in feet, andthe second number is the number of stages in the Marx generator. Asshown in FIG. 16, the generators are relatively compact in size for theenergy delivered. Also, the time to design and build such generators isrelatively short. For example, the PI14-80 was recently designed andbuilt in eight months. As shown in FIG. 17, the cost of the technologyis relatively inexpensive. State of the art generators produce a 16 to20 MeV, 400 to 800 kA electron beam with a pulse width of approximately100 ns. The overall electrical efficiency for such a generator isapproximately 40% to 45%. If the energy remaining in the Marx generatoris recovered, the energy efficiency of such a generator is 80% to 90%.

As shown in FIG. 18, high-impedance generators are composed of fivebasic components. A dc charging system 116 is used to charge the Marxgenerator 118, which is the primary energy storage component. The Marxgenerator 118 consists of a large number of stages which are charged inparallel and discharged in series using spark gap switches. FIG. 19schematically illustrates the electrical equivalent of a Marx stagewhich consists of two capacitances 126 and 128 connected in series witha center ground to allow positive and negative dc charging.

The Marx generator is then used to charge a Blumlein 120 such asschematically illustrated in FIG. 20. A Blumlein 120 is essentially twocoaxial transmission lines 130 and 131 connected in series with thediode impedance 134 Z_(D). Physically, the Blumlein appears as threeconcentric, annular conductors. This folded configuration is used toreduce the spatial dimension of the Blumlein. In operation, the centerconductor 132 is charged through an inductor 138 having an inductanceL_(c) which appears as a short. Once charged, the switch 136 is closedand the transmission line 131 begins to discharge with a pulsepropagating toward the diode 134. When the pulse hits the impedancediscontinuity (Z_(D)) of diode 134, a voltage appears across the diode134. As opposed to the shorted transmission line 131, which has animpedance Z_(I), the transmission line 130 with impedance Z_(O), isopen. Thus, for a properly matched configuration (Z_(O) =Z_(I) =Z_(D)/2), a voltage equal to charge voltage on the inner conductor 132appears across the diode 134 for a period twice the propagation timedown any one of the transmission lines 130 or 131. The inductor 138appears as an open circuit during the Blumlein discharge. For highvoltages the Blumlein 120 uses transformer oil as a dielectric.

Due to the physical configuration of the Blumlein 120, it is difficultto design the transmission lines 130 and 131 such that Z_(I) =Z_(O). Asa result, there is typically a very small, but nonnegligible, voltagethat appears across the diode 134 during the Blumlein charge, due tostray capacitances and inductances which is referred to as a prepulse.From the standpoint of proper operation of a high-current density diode,this prepulse must be suppressed. Significant progress in prepulsesuppression has occurred in the past few years. Through the use ofprepulse switches 122 combined with careful design of the feed and dioderegion, a prepulse of less than 50 kV has been demonstrated for a 9 MVBlumlein charge. With this advance in prepulse suppression, beamparticle densities exceeding 10¹⁴ electrons/cm³ have been obtained in afocused flow configuration. More recently, however, a techniqueutilizing water as a dielectric, rather than oil in a Blumleinconfiguration, has been developed by Maxwell Laboratories of San Diego,Calif., which reduces prepulse voltage to less than 1 kV formulti-megavolt beams. This very low prepulse voltage provided by theMaxwell Laboratories configuration appears to be the preferred method ofoperation.

The final component is the diode 124, which can be either foil orfoilless. Foil diodes suffer rapid impedance collapse when the currentdensity exceeds 20 kA/cm². The physics of this problem has not, however,been considered in a systematic fashion and current densities up to 100kA/cm² should be obtainable with improved vacuum systems.

Foilless diodes are naturally suited for embodiment of the presentinvention illustrated in FIGS. 39 and 40 since annular beams are readilyproduced at high current densities. However, the operation and flowcharacteristics of such diodes could be significantly advanced. Adetailed discussion of the potential of the foilless diode is disclosedin Los Alamos Scientific Report LA-7169-P by Lester E. Thode entitled "AProposal for Study of Vacuum Adiabatic Compression of a RelativisticElectron Beam Generated by a Foilless Diode."

Pulsed high-current electron beams with particle energy exceeding 20 MeVcan be produced with a multigap accelerator, as schematicallyillustrated in FIG. 21. The multigap accelerator is basically a linearaccelerator with radial transmission lines or Blumleins providing energyto the accelerating gaps 146. Radial lines 140 are composed of coaxialdisk or cone conductors which are stacked in series. As a result, theaccelerator is amenable to mass production, probably at a cost of lessthan $5/joule delivered. In addition, the development time of a 200 to800 kJ, 5 to 20 TW, 10 to 100 cycle per second prototype accelerator isless than five years. The injector 144 for such an accelerator can bethe high-current electron beam generator disclosed infra, or the firstaccelerating stage of the accelerator. Fabrication of such acceleratorsis disclosed by A. I. Pavlovskii et al., Sov. Phys.--Dokl. 20, 441(1975), in an article entitled "Multielement Accelerators Based onRadial Lines."

Referring again to FIGS. 11 and 12, the relativistic electron beams 34and 76 propagate along the vacuum drift tube and adiabatic compressors36 and 78 to the modulators 38 and 80. External solenoidal magneticfield sources 40 and 82 generate a magnetic field in the generatordiode, accelerator, drift tube, and modulator regions to ensure alaminar flow beam equilibrium. In the vacuum drift tubes 36 and 78, thestrength of the external magnetic field can be increased along thedirection of beam propagation to produce adiabatic beam compression.Modest compression ratios can reduce the beam radius a factor of 2 to 3,while preserving a laminar flow equilibrium, provided the compression iscarried out in vacuum. Vacuum systems 42 and 84 maintain the requiredvacuum.

Modulators 38 and 80 constitute an inner portion of the vacuum drifttubes 36 and 78 and are formed by a periodic structure or dielectricalong the direction of beam propagation. Alternatively, a rippledmagnetic field could be utilized to weakly bunch the beam. The purposeof modulators 38 and 80 is to provide an enhanced narrow band noiselevel (very weak modulation) at a wavelength and phase velocity slightlybelow the natural wavelength and phase velocity of the instability inthe target plasma.

The underlying idea behind this weak modulation is increased couplingefficiency. For waves propagating along the relativistic electron beamaxis, the characteristic growth rate δ/ω_(P) and characteristic changein beam velocity δβ=2(β-ω/kc) for the streaming instability as afunction of the wave number k=2π/λis shown in FIG. 22. Here ω/k is thephase velocity associated with the electrostatic spectrum, and v is theinitial beam velocity. The growth rate is normalized to the plasmafrequency ω_(p). For an unmodulated beam the nonlinear evolution of thestreaming instability is determined by the fastest growing wave, whichoccurs at kv/ω_(P) =1.1 in this example. The beam energy loss isdetermined by

    δγ/γ≅γ.sup.2 βδβ(unmodulated)/[1+γ.sup.2 βδβ(unmodulated)]≅S/(1+S)       (11)

as described previously.

By enhancing the noise level at a wavelength and phase velocity slightlyshorter and slightly lower than the fastest growing wave, the beamenergy loss is determined by δβ(modulated) shown in FIG. 22. Thecoupling efficiency is then increased to

    δγ/γ≅γ.sup.2 βδβ(modulated)/[1+γ.sup.2 βδβ(modulated)]≅χS/(1+χS), (12)

where χ≅1.0 to 1.3 based upon analysis of the modulated interaction.Physically, the modulation leads to an enhanced strength parameter (χS).The modulation also reduces the effect of foil scattering and collisionson the interaction.

The low-density gas chambers 52 and 94 provide isolation between thereplaceable target plasma containers 66 and 108 and modulators 38 and80, drift tube and adiabatic compressors 36 and 78, accelerators 32 and74, and generators 30 and 72 of figures 11 and 12, respectively. Theelectron density in the ionized low-density plasma channels 46 and 88 istypically close to the relativistic electron beam density, whereas inthe target plasmas 68 and 112 the electron density is 4 to 6 orders ofmagnitude above the beam density. The low-density gases 50 and 92comprise either H₂, He, Ar, N₂ or residual gas associated with theprevious operation of the system.

Foils 44 and 86 provide isolation between the vacuum modulators 38 and80 and the low-density plasma channels 46 and 88, and convert a smallfraction of the rising beam impulse into Bremsstrahlung radiation whichis directed predominantly along the direction of beam propagation. Theisolation function is provided by a layer of metal (titanium, aluminum,or beryllium), graphite, or plastic, such as mylar (C₁₀ H₈ O₄), kapton(C₂₂ H₁₀ N₂ O₅), or polycarbonate. A layer of plastic impregnated withhigh Z atoms, a fine mesh high Z wire screen with a very high opticaltransparency, or a high Z aperturing layer can be used to provide theBremsstrahlung radiation. Bremsstrahlung radiation generated in thismanner, aids in the creation of low-density plasma channels 46 and 88for beam propagation through the low-density gases 50 and 92. Withadvances in relativistic electron beam technology, foils 44 and 86 canbe eliminated in favor of strong differential pumping of the modulatorregions 38 and 80.

Foils 48 and 90, provide isolation between the low-density plasmachannel 46 and the dense target plasma and are constructed in a fashionsimilar to foils 44 and 86. Foils 48 and 90 also act to initiate thecollective interaction and generate Bremsstrahlung radiation for partialionization of the dense plasma target to assist or replace preionizers62 and 64, 104 and 106.

In the ionized low-density plasma channels 46 and 88 and in the targetplasma, the self fields of the beam are shorted out so that an externalmagnetic field is not required to achieve beam equilibrium. Thus, thebeam can be ballistically guided through low-density plasma channels 46and 88 to the plasma target. However, the overall efficiency of thesystem is enhanced by the presence of external magnetic field sources 70and 110. Also, external magnetic field sources 70 and 110 provideincreased stabilization of the relativistic electron beam withinlow-density plasma channels 46 and 88, respectively.

Preionizers 62 and 64, 104 and 106 provide full ionization of targetplasmas 68 and 112, respectively. Any number of devices for creating afully-ionized gas, such as discharge tubes, channel forming wires,various lasers including electron beam driven free electron lasers,plasma guns, microwave generators, or low-energy particle beams, can beused. The laser, however, is the best device for creating alow-temperature, fully-ionized plasma in the 10¹⁷ to 10²⁰ electrons/cm³density region.

With a laser preionizer, windows 54 to 60 and 96 to 102, formed fromsapphire, salt, or other appropriate materials, are positioned in thelow-density gas chambers 52 and 94 and target plasma containers 66 and108, respectively. For a fully-ionized target density of 8×10¹⁸ to 10²⁰electrons/cm³, a 0.1 μs to 2.0 μs, 0.2 kJ to 10 kJ HF laser, or a numberof smaller HF lasers, can be used as preionizers 62 and 64, 104 and 106.A 0.1 μs to 2.0 μs, 0.2 kJ to 3 kJ CO₂ laser, or a number of smaller CO₂lasers, are appropriate for fully ionizing gases with densities lessthan 8×10¹⁸ electrons/cm³.

The combination of Bremsstrahlung radiation produced at foils 48 and 90,direct impact ionization by the beam, avalanche, and the initialcollective interaction is capable of fully ionizing the target plasma.However, the beam requirements are more stringent when the relativisticbeam provides both ionization and heating of the target plasma. Use ofpreionizers 62 and 64, 104 and 106, therefore lowers the relativisticelectron beam technology requirements.

The anomalous pinch, as disclosed in the above referenced copendingapplication Ser. No. 882,024 filed Feb. 28, 1978 and illustrated in FIG.11, is the simplest mode of operation. The relativistic electron beamtarget is a simple gas-filled container of DT, DD or HB. As a neutronsource, the anomalous pinch intrinsically requires a very high-densityplasma of at least 10¹⁹ electrons/cm³.

As an alternative approach to a pulsed neutron source, the anomalouspinch can be operated as a target for an intense deuterium beamgenerated by the rapidly developing pulse power light-ion beamtechnology. Operating with a plasma density of approximately 10¹⁸electrons/cm³, the plasma electron temperature can be elevatedsufficiently to reduce the cross section for deuterium beam energyabsorption by target plasma electrons. Thus, the probability of survivalof trapped energetic deuterium ions to undergo fusion with the plasmadeuterium and tritium ions is significantly enhanced. Although this twocomponent concept is old, intense neutron pulses can be produced usingpresent pulse power technology.

The device of FIG. 11 operates by applying the relativistic electronbeam 34 to low-density gas chamber 52 such that beam 34 penetrates foil48 with negligible scattering and initiates convective wave growth suchthat the waves e-fold until saturated through nonlinear trapping of thebeam electrons. Since the nonlinear waves are not normal plasma modes,they are absorbed into the plasma very rapidly through nonlinear modebeating. Actually, this nonlinear mode beating acts throughout theentire interaction and keeps the level of electric field energyrelatively low compared with the energy transferred from the beam to theplasma. The presence of the foil 48 thus ensures that the beam energy isdeposited at a specified location within the target plasma container 66,as opposed to moving upstream.

Since energy and momentum are being transferred from relativisticelectrons 34 to nonrelativistic electrons within the target plasma 68,the beam both heats and drives an axial current in the target plasma.The presence of the axial current, in turn, initiates plasma energyconfinement through the generation of an azimuthal magnetic fieldsimilar to a Z pinch. Taking into account increased internal pressureresulting from the nonohmic process, an equilibrium pinch configurationis formed with currents in the multi-megampere range, with significantreduction in heat conduction losses. Relative to the typical classicalZ-pinch, the generation of the anomalous pinch is considerably faster.

For a solid relativistic electron beam schematically illustrated in FIG.11, the anomalously generated aximuthal magnetic field 150 and heatedplasma column 148 is illustrated in FIG. 23. The axial nonuniformity inthe azimuthal magnetic field strength of azimuthal magnetic field 150 issimilar to the energy deposition illustrated in FIG. 6. Primary energyloss from the anomalous pinch is indicated by arrows. The presence of anexternal axial magnetic field and proximity of the radial wall, togetherprovide stable operation.

FIG. 24 is a schematic illustration of the arrangement schematicallydisclosed in FIG. 11 and disclosed in the above referenced copendingapplication Ser. No. 882,024 filed Feb. 28, 1978 for producing ananomalous pinch. As shown, relativistic electron beam generator 152produces a solid relativistic beam 154 which propagates through thevacuum tube and adiabatic compressor 156 and adjacent modulator 158. Therelativistic electron beam 154 then penetrates foil 160, passes throughthe low-density plasma channel 162, penetrates foil 164, and anomalouslytransfers a fraction of its energy and momentum to the target plasma 170to generate the anomalous pinch illustrated in FIG. 23. Windows 172 and174 allow the laser ionization beam 178 to penetrate the target plasmacontainer 168 and low-density gas chamber 166. A salt or sapphire windowis used for CO₂ or HF lasers, respectively. An ionization beam intensityof 10⁹ to 10¹⁰ watts/cm² is sufficient to fully ionize the plasma.

A fully-ionized plasma with sufficient axial uniformity can be formedusing the configuration shown in FIG. 24. The laser energy istransferred to the target plasma through inverse Bremsstrahlung.Consequently, the target plasma exhibits a slightly decreasing gradientalong the direction of propagation of the relativistic electron beam154. Such a decreasing gradient tends to increase the strength of thedeposition, since its effect on the nonlinear dynamics is similar topremodulation. In fact, the ability of the streaming instabilities tocounteract self-consistent plasma hydrodynamic gradients is related tothis dynamic effect.

FIG. 25 is an alternative arrangement in which two lasers 208 and 210apply ionization beams 212 and 214 transverse to the axis of therelativistic electron beam 182. Windows 204 and 206 in the low-densitygas chamber 194 and windows 200 and 202 in the target plasma container196 allow passage of the ionization beams to the target plasma 198.

FIG. 26 is a schematic end view of an additional alternative arrangementutilizing three lasers 234, 236, and 238 which produce ionization beams240, 242 and 244. Windows 228, 230 and 232 in the low-density gaschamber 216 and windows 222, 224 and 226 in the target plasma container218 provide ionization beams 240, 242 and 244 access to the targetplasma 220. The advantage of the arrangement shown in FIG. 26 is thatlasers 234, 236 and 238 are arranged in an off-axis position such thatlaser beams 240, 242 and 244 are not directed at other lasers.

Although the single laser beam configuration shown in FIG. 24 producesthe desired target plasma, additional magnetic field energy is requiredto deflect the residual relativistic electron beam so that the electronbeam does not impinge upon laser 176. Also, the cost and technologyassociated with a single large laser is greater than with a number ofsmaller lasers with the same combined energy. Thus, the multiple laserconfigurations shown in FIGS. 25 and 26 are considered the preferredmethod of operation.

The preceding laser configurations are also appropriate for systemswhich use the high-energy density plasma to drive a fast liner toconvergence or to implode a structured microsphere as disclosed in theabove referenced copending applications Ser. No. 9,703 filed Feb. 5,1979 and Ser. No. 9,702 filed Feb. 5, 1979, and schematically shown inFIG. 12. Since the laser intensity is quite low, the hot electronspectrum generated by such a beam interacting directly with a powermultiplication device is negligible. The components of FIG. 11 and theiroperation are identical to the components of FIG. 12 with the exceptionof the target plasma container 66 and relativistic electron beam 34.Similarly, the deposition of electron beam energy in the target plasma112 occurs in the same manner described with respect to FIGS. 5, 6, 11and 22 to 26. Therefore, the remaining disclosure of FIGS. 27 through 38relates only to the manner in which a hot annular plasma 112 drives afast liner to convergence or to implode a structured microsphere.

Historically, high explosives or magnetically driven thin, cylindricalmetallic shells have been referred to as liners. These hybrid devicesincorporate concepts common to both magnetic and inertial confinement ofplasma. Liners have been used to compress magnetic fields, compress andheat magnetically confined plasmas, and generate radiation. This type ofpower multiplication device can be generalized to include spherical andellipsoidal shapes. Since the liners and multilayer in design, they aremuch like laser fusion pellets.

A configuration suitable for driving fast spherical or cylindricalliners such as disclosed in copending application Ser. No. 9,703 filedFeb. 5, 1979 is shown in FIGS. 27 and 28, respectively. Here, a singlelaser ionization beam 252 entering through window 254 is used. Multiplelaser ionization configurations, as shown in FIGS. 25 and 26, may beemployed to obtain full ionization. The use of lasers for preionizationlowers the relativistic electron beam technology requirements asdisclosed above. Thus, the laser ionization sources should be consideredas optional.

Referring again to FIGS. 27 and 28, an annular relativistic electronbeam 260 which corresponds to beam 76 produced by the device of FIG. 12,penetrates the initiation foil 246, which also acts as an end plug tocontain the low-temperature plasma or gas. As the voltage and currentdensity rise, the anomalous coupling coefficient increases to itsoptimal value, and the beam transfers a large fraction of its energy andmomentum to the annular plasma region 258. The beam driven azimuthalmagnetic field 256, in turn, directs the annular plasma thermal energyto the fast spherical liner 250 or fast cylindrical liner 262. Since thesource of the azimuthal magnetic field 256 is the result of an axialcurrent flow in the annular plasma 258, magnetic field 256 is notpresent in the vicinity of the fast spherical liner 250 or fastcylindrical liner 262. The presence of an axial external magnetic fieldgenerated by external magnetic field source 110 shown in FIG. 12, can beused to increase the anomalous coupling coefficient. However, since theannular plasma column 258 is very high beta, the external magnetic fieldproduced by source 110 is excluded during operation.

The radial wall of the plasma target container 248 is sufficiently thickto ensure magnetic flux containment and sufficiently massive to provideradial inertial confinement (tamper) on the relativistic electron beamtime scale, i.e. ≲100 ns. Thus, radial energy loss to the container wallis limited by both the azimuthal magnetic field 256 and excludedexternal magnetic field produced by source 110. Heat conduction islimited axially on the beam time scale by the lower axial temperaturegradient, azimuthal magnetic field 256, and self-mirroring of theexternal magnetic field 110. Thus, the geometry takes advantage ofanomalous coupling and classical heat conduction to rapidly andefficiently remove energy from the relativistic electron beam 260 andtransport it to the fast liner.

A cross-sectional view of the basic configuration with dual laserionization beams 268 and 270, 282 and 284 for driving fast liners asdisclosed in the above referenced copending application Ser. No. 9,703filed Feb. 5, 1979, is shown in FIGS. 29 and 30, respectively. In thisconfiguration, windows 264 and 266, 278 and 280 are placed in the radialwall of the plasma container. The heated annular plasmas 274 and 286drive the spherical and cylindrical fast liner to implosion by explosiveor ablative means as disclosed previously.

Detail of the fast spherical liner 250 and fast cylindrical liner 262 asdisclosed in the above referenced application Ser. No. 9,703, filed Feb.5, 1979, is shown in FIGS. 31 and 32, respectively. Each of the fastliners consists of ablators 292 and 298, pushers 294 and 300 and solidbuffers 296 and 302. The ablator is boiled off through heat conduction,to propel the pusher and solid buffer to high-implosion velocity. Sincethe thermal conductivity of a plasma is a strong function oftemperature, the rate at which energy is transported to the linerincreases in time throughout the beam pulse. Thus, some natural shapingof the plasma driving source is obtained. Such shaping leads to strongercompression and heating of the gas fuel 272 and 288, as disclosed by R.J. Mason et al., Phys. Fluids 18, 814 (1975) and S. D. Bertke et al.,Nucl. Fusion 18, 509 (1978).

Structured spherical pellets similar to the liner 250 have been studiedextensively with respect to laser implosion. The ablators 292 are 298 ofboth the spherical and cylindrical liners are a low Z, low mass densitymaterial such as LiDT, Be, ND₃ BT₃, boron hydride, or CDT. Pushers 294and 300 are typically a higher Z and mass density material such asglass, aluminum, gold, or nickel. Plastic embedded with high Z atoms isalso used. Solid DT or LiDT can be used for the solid buffers 296 and302. Depending upon the desired implosion velocity and various stabilityconsiderations, the total mass of fast liner 250 and 262 varies from 1to 100 milligrams.

In the case of the cylindrical liner 262, shaping minimizes loss of theenclosed fuel 288 out the ends, as shown in FIG. 32. Alternatively, theends can be plugged if the annular plasma 286 and fuel 288 aredifferent. For example, gas fuel 272 and 288 may comprise DT, DD, DHe³,HLi⁶, or HB¹¹ whereas target plasma 274 and 286 may comprise H₂, He, DT,DD, or other low Z gas. An ellipsoidal shaped liner can also be used.

FIG. 33 illustrates another embodiment utilizing a fast liner. Accordingto FIG. 33, a solid beam penetrates foil 320 to form an anomalous pinch318 within the cylindrical liner 262, which is, in turn, driven by anannular beam entering through foil 304. Deflector 306 provides initialionization in the anomalous pinch region 318. The cylindrical liner 262implodes upon the plasma 318 to enhance compression and burn.

Target geometry, utilizing two annular relativistic electron beams todrive a spherical liner 250 is schematically illustrated in FIG. 34. Inoperation, beam deflection is minimized as beams 362 and 328 passthrough the beam driven azimuthal magnetic field regions, as indicatedin FIG. 14.

The approach of obtaining an intense radiation, neutron and/or alphaparticle source disclosed in the above referenced copending applicationSer. No. 9,702 filed Feb. 5, 1979, by Lester E. Thode is to use ahigh-density, multi-kilovolt relativistic electron beam produced plasmato drive a fast liner, which then produces an intense, shaped energypulse suitable for imploding a structured microsphere such as disclosedR. J. Mason, Phys. Fluids 18, 814 (1975) and Los Alamos ScientificReport LA-5898-MS (October 1975), S. D. Bertke et al., Nucl. Fusion 18,509 (1978), and G. S. Fraley et al., Phys. Fluids 17, 474 (1974). Such amicrosphere can be filled with either DT, DD, DHe³, HLi⁶, or HB¹¹, orsome mixture thereof for example.

The basic geometry of the approach disclosed is illustrated in FIGS. 35and 36, for a single laser ionization beam 340 entering through window342. The multiple laser ionization configurations as shown in FIGS. 25and 26 can also be used. As pointed out above, the use of lasers forpreionization, lowers the relativistic electron beam technologyrequirements. Therefore, the laser ionization sources should beconsidered as optional.

An annular relativistic electron beam 344 penetrates the initiation foil346, which also acts as an end plug to contain the low-temperatureplasma. As the voltage and current density rise, the anomalous couplingcoefficient increases to its optimal value, and the beam transfers alarge fraction of its energy and momentum to the annular plasma region348. The beam driven azimuthal magnetic field 350 in turn directsannular plasma 348 thermal energy to the fast spherical line 352 of FIG.35 or fast cylindrical liner 354 of FIG. 36. Since the source of theazimuthal magnetic field 350 is the result of an axial current flow inthe annular plasma 348, resulting from conservation of momentum, theazimuthal magnetic field 350 is not present in the vicinity of the fastspherical liner 352 or fast cylindrical liner 354. The presence of anaxial external magnetic field generated by source 110 of FIG. 12 can beused to increase the anomalous coupling coefficient. However, since theannular plasma column 348 and plasma engulfing the liner are very highbeta, the external magnetic field generated by source 110 of FIG. 12 israpidly excluded.

The radial wall of the plasma target container 356 is sufficiently thickto ensure magnetic flux containment and sufficiently massive to provideradial inertial confinement (tamper) on the relativistic electron beamtime scale, i.e. ≲100 ns. Thus, radial energy loss to the container wallis limited by both the azimuthal magnetic field 350 and excludedexternal magnetic field generated by source 110 of FIG. 12. Heatconduction is limited axially on the beam time scale by the lower axialtemperature gradient, azimuthal magnetic field 350, and self-mirroringof the external magnetic field generated by source 110. Thus, thegeometry takes advantage of anomalous coupling and classical heatconduction to rapidly and efficiently remove energy from therelativistic electron beam 344 and transport that energy to the fastliners 352 and 354.

As shown in FIGS. 37 and 38, the fast liners 352 and 354 consist ofablators 360 and 362, pushers 364 and 366, and solid buffer 368 or 370.The ablator is boiled off through heat conduction, with the pusher andsolid buffer propelled to high implosion velocity. The ablators 360 and362 are low Z, low mass density material such as LiDT, Be, ND₃ BT₃,boron hydride, or CDT. Pushers 364 and 366 are typically a higher Z andmass density material such as glass, aluminum, gold, nickel or plasticembedded with high Z atoms. Solid DT or LiDT can be used for solidbuffers 368 and 370. Depending upon the implosion velocity desired andstability considerations, the total mass of fast liners 352 and 354illustrated in FIGS. 37 and 38, respectively, is from 1 milligram to 100milligrams. Also, the driver gs 372 and 374 of FIGS. 37 and 38,respectively, may comprise DT, DD, or higher Z gas such as N₂, Ar, orKr.

In operation, as the liner collapses, the density and temperature ofbuffer gases 372 and 374 in contact with the microsphere 358, increasesin time. Such pulse shaping, which is different for fast spherical liner352 and fast cylindrical liner 354, allows shock overtaking as pointedout in the above reference articles by R. J. Mason et al. and S. D.Berke et al., producing high compression of the ablatively drivenmicrosphere 358. Using the high-density thermal gas 372 and 374 of FIGS.37 and 38, respectively, for implosion, reduces the preheating problemassociated with the microsphere 358.

Basic detail of the microsphere 358 is shown in FIGS. 37 and 38. Thematerials used for ablators 376 and 378, pushers 380 and 382, solidbuffers 384 and 386, and gas fuel 388 and 390 are similar to those setforth for liners 352 and 354. Also, multiple pusher configurationsutilizing velocity multiplication to obtain very high implosionvelocities can also be incorporated into the structural microsphere 358.

Various radiation devices, according to the present invention, can befabricated depending upon the specific application for the device.Basically, the concept of one embodiment of the present invention is togenerate a kilovolt high-density plasma to heat high Z materials ofvarious sizes and shapes to generate radiation.

For example, FIGS. 39 and 40 illustrate a soft x-ray source in which awire array is engulfed by a high-density, multi-kilivolt plasma 390produced by an annular relativistic electron beam such as beam 76illustrated in FIG. 12. The device of FIGS. 39 and 40 could be directlyattached to the drift tube 78 or modulator 80 of FIG. 12.

The target plasma container 394 is a simple cylinder which is lined witha high Z material 396. A beryllium window 398 is provided for radiationextraction. A wire array 392 is supported by the initiation foil 400 andend plug 402. The size, shape, and number of wires in the array 392depends upon the opacity of the materials. Wires of aluminum, titanium,tantalum, tungsten, or stainless steel with diameters of 5 to 100 μmappear suitable. Such an array is designed to have has a low opacity inthe direction of the beryllium window 398.

Due to the compact size and directional properties of the above deviceit can be operated as a module in a configuration producing megajoulelevel radiation with a 10 ns to 100 ns pulse length. Additionally,either annular or solid relativistic electron beams can be utilizeddepending upon the particular array of high Z material used.

Moreover, a moderate Z gas such as N₂ or Ar or a mixture of low Z gassuch as H₂ and high Z gas such as Kr or Xe with an electron density of10¹⁷ -10¹⁹ electrons/cm³, can be used as the target plasma 68 of thedevice of FIG. 11 to produce radiation. In the radiation mode, berylliumwindows in the target plasma container are used and the low-density gaschamber 52 of FIG. 11 is eliminated. Such a tunable radiation source issuitable for a variety of applications and can be used with a solid beamas illustrated in FIG. 11 or an annular beam as illustrated in FIG. 12.Also, the frequency of the radiation can be adjusted by varying theplasma temperature.

The present invention therefore provides a device for producing intenseradiation which is easy to implement within current technologicallimitations. By optimizing the extremely powerful streaminginstabilities to heat the high-density plasma with the relativisticelectron beam according to method (a), the present invention providesefficient deposition of beam energy to heat the plasma to multi-kilovolttemperatures to, in turn, heat the high Z materials to produce anintense source of radiation.

Also, the present invention provides a tunable source of intenseradiation utilizing a moderate Z gas such as N₂ or Ar as the targetplasma which is easy and inexpensive to implement with currentlyavailable technology.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described and thatsubject matter disclosed herein shall not be precluded from being laterclaimed in the present application or a continuation,continuation-in-part, or reissue application.

What is desired to be secured as Letters Patent of the United States is:
 1. A device for generating radiation comprising:means for generating relativistic electron beam having a voltage of at least 3 MeV, a current density of at least 1 kA/cm² and (N re)/(1-v² /c²)1/2≦1 where N is the line density of beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light, a target plasma chamber containing a high-density gas; a high Z material disposed in said target plasma chamber; means for ionizing said high-density gas to generate a high-density plasma; means for initiating convective oscillations in said plasma upon application of said relativistic electron beam such that streaming instabilities are produced in said plasma causing electron beam energy to be deposited in said plasma to heat said plasma to kilovolt temperatures and heat said high Z material to generate an intense source of radiation.
 2. The device of claim 1 wherein said high Z material comprises a wire array.
 3. A device for producing energy in the form of radiation comprising:a high-density plasma disposed within a target chamber; a high Z material disposed within said target chamber; means for producing relativistic electron beam having a current density of at least 1 KA/cm² and a (N re)/(1-v² /c²)1/2≦1 where N is the line density of beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light, and having a voltage of at least 3MeV, which beam is sufficient to penetrate said target chamber and initiate convective oscillations in said high-density plasma such that energy is transferred from said relativistic electron beam to said plasma to heat said plasma to kilovolt temperatures which, in turn, heats said high Z material to generate said radiation.
 4. The device of claim 3 wherein said high-density plasma comprises DT.
 5. The device of claim 3 wherein said high-density plasma comprises DD.
 6. The device of claim 3 wherein said high-density plasma comprises H₂.
 7. The device of claim 3 wherein said high Z material comprises a wire array.
 8. An x-ray device comprising:means for retaining a high-density gas within a predetermined volume; means for ionizing said gas to produce a high-density plasma; a high Z material disposed within said means for retaining said high-density gas; means for generating relativistic electron beam having at least a 3MeV voltage sufficiently high to overcome classical scattering upon penetrating said means for retaining said high-density gas so as to generate streaming instabilities in said high-density plasma causing said relativistic electron beam to heat said high-density plasma to kilovolt temperatures to heat said high Z material to generate x-rays and having a current density of at least 1 KA/cm² and (N re)/(1-v² /c²)1/2≦1 where N is the line density of the beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light.
 9. The x-ray device of claim 8 wherein said relativistic electron beam is an annular relativistic electron beam surrounding said high Z material.
 10. The x-ray device of claim 9 wherein said high Z material comprises a wire array.
 11. The x-ray device of claim 8 wherein said relativistic electron beam comprises a solid beam surrounded by said high Z material.
 12. The device of claim 8 wherein said high-density plasma comprises DT.
 13. The device of claim 8 wherein said high-density plasma comprises DD.
 14. The device of claim 8 wherein said high-density plasma comprises H₂.
 15. A method of producing radiation comprising:confining a high-density gas within a target chamber; ionizing said gas to produce a high-density plasma; generating an annular relativistic electron beam having at least a 3 MeV voltage sufficiently high to penetrate said target chamber without scattering to produce streaming instabilities in said plasma causing said electron beam to heat said high-density plasma to kilovolt temperatures which, in turn, heats a high Z material to generate radiation and having a current density of at least 1 KA/cm² and (N re)/(1-v² /c²)1/2≦1 where N is the line density of beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light.
 16. A device for generating radiation comprising:means for generating relativistic electron beam having a voltage of at least 3 MeV, a current density of at least 1 kA/cm² and (Nre)/(1-v² /c²)1/2≦1 where N is the line density of the beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light, a target plasma chamber containing a high-density Z gas; means for ionizing said high-density gas to generate a plasma; means for initiating convective oscillations in said plasma upon application of said relativistic electron beam such that streaming instabilities are produced in said plasma causing electron beam energy to be deposited in said plasma to heat said plasma to kilovolt temperatures and generate radiation.
 17. The device of claim 16 wherein said high-density gas comprises Ar.
 18. The device of claim 16 wherein said means for ionizing said high-density gas comprises at least one laser.
 19. The device of claim 16 wherein said high-density gas comprises a mixture of high Z gas and a low Z gas.
 20. The device of claim 19 wherein said high Z gas comprises Kr and said low Z gas comprises H₂.
 21. The device of claim 16 wherein said means for initiating convective oscillations comprises a thin, low-density foil.
 22. A device for producing energy in the form of radiation comprising:a high-density plasma disposed within a target chamber; means for producing relativistic electron beam having a current density of at least 1 KA/cm² and (N re)/(1-v² /c²)1/2≦1 where N is the line density of the beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light and a having, a voltage of at least 3MeV, which beam is sufficient to penetrate said target chamber and initiate convective oscillations in said high-density plasma such that energy is transferred from said relativistic electron beam to said plasma to heat said plasma to kilovolt temperatures and generate radiation.
 23. The device of claim 22 wherein said relativistic electron beam is a solid beam.
 24. The device of claim 22 wherein said relativistic electron beam comprises an annular beam.
 25. A radiation device comprising:means for retaining a high-density gas within a predetermined volume; means for ionizing said gas to produce a high-density plasma; means for generating electron beam having at least a 3MeV voltage sufficiently high to overcome classical scattering upon penetrating said means for retaining said high-density gas so as to generate streaming instabilities in said high-density, plasma causing said relativistic electron beam to heat said high-density plasma to kilovolt temperatures to generate a tunable source of radiation and having a current density of at least 1 KA/cm² and (N re)/(1-v² /c²)1/2≦1, where N is the line density of the beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light.
 26. The device of claim 25 wherein said high-density gas comprises a mixture of a high Z gas and a low Z gas.
 27. The device of claim 26 wherein said high Z gas comprises Kr and said low Z gas comprises H₂.
 28. The device of claim 25 wherein said high-density, gas comprises Ar.
 29. A method of producing radiation comprising:confining a high-density gas within a target chamber; ionizing said gas to produce a high-density plasma; generating an annular relativistic electron beam having at least a 3MeV voltage sufficiently high to penetrate said target chamber without scattering to produce streaming instabilities in said plasma causing said electron beam to heat said high-density, plasma to generate a tunable source of radiation and having a current density of at least 1 KA/cm² and (N re)/(1-v² /c²)1/2≦1, where N is the line density of the beam electrons, re is the classical electron radius, v is the beam velocity and c is the speed of light.
 30. The method of producing radiation according to claim 29 further comprising the step of:varying the temperature of said high-density plasma to tune said source of radiation to various frequencies. 